Thanks guys! Yeah it's a weird issue for sure and likely very rare, so it's probably not a big deal. If it helps for reproducing it, here's a few notes:
27 apps installed at the time of backup/restore
Backup & Restore used tgz format with OVH Object Storage in BHS region
Backup from a LunaNode m.8 model in Toronto region
Restored onto OVH b2-7 model (though since upgraded to b2-15) in BHS3 region
LunaNode instance (source) was running Ubuntu 18.04 at backup time, and OVH instance (target) was running Ubuntu 20.04 at the time of restore.
When I restored, I very nearly ran out of disk space on the included disk, leaving only ~ 1.5 GB of space remaining.
When restoring initially, it failed to restore because of the issue I reported earlier, though doubtful this is a root cause. Immediately moved the boxdata to external disk afterwards though, so plenty of space free soon after the restore was done once I moved boxdata off (20 GB in emails alone so it takes up a lot of space).
Hopefully those notes above help in some small way. No worries though if you can't reproduce it, I imagine it's a very rare scenario and could have even been completely unique to me somehow. Hopefully others can chime in though if they experienced anything similar where cron wouldn't run at all (whether a restore involved or not, as I'm still not 100% certain it had to do with the restore though I presume it did).